Applicant claims, under 35 U.S.C. § 119, the benefit of priority of the filing date of Jun. 25, 2005 of a German patent application, copy attached, Serial No. 10 2005 029 553.3, filed on the aforementioned date, the entire contents of which is incorporated herein by reference.
1. Field of Invention
The present invention relates to a position measuring arrangement, having a scale, a scanning head, and a control device for comparing an amplitude of the scanning signal with a predetermined level. The present invention further relates to a method for controlling scanning signals.
2. Discussion of Related Art
The control of position-dependent scanning signals of a position measuring arrangement is necessary in particular during the mounting of the position measuring arrangement or after the position measuring arrangement has been mounted in order to assure the longest possible measuring operations. The signal quality and the measurement accuracy are considerably dependent on the exact adjustment of the scanning head in relation to the scale. In order to assure a high degree of measuring accuracy in connection with an incremental position measuring arrangement, the scanning signal generated by the scanning head should have a high and level amplitude, as well as a mutual phase shift φ of 90°. The amplitude is affected by the distance between the scanning head and the scale, and the phase shift by the tilt of the scanning head relative to the measuring direction.
These parameters of the analog scanning signals can be represented very well by an oscilloscope. To this end the two scanning signals, which have been phase-shifted by 90° in relation to each other, are fed to the two channels of a dual-beam oscilloscope, so that a Lissajous figure is created on the display screen. The radius of the Lissajous figure constitutes a measurement of the amplitudes, as well as the phase relationship, of both scanning signals.
For simplifying the checking of position-dependent scanning signals, a position measuring arrangement has been proposed in EP 0 514 081 B1, which is laid out for controlling the amplitude of analog scanning signals. The position measuring arrangement contains a first control device which makes a differentiation as to whether the amplitude is located above or below a predetermined level, wherein the level corresponds to an error level, below which the scanning signal is not dependable, but above which the scanning signal is dependable and can be used for position measuring. It has been found that the control of a correct installation of a position measuring arrangement is not possible by this error level. Therefore, for controlling the correct installation, a second error level was used for comparison with the amplitude of the scanning signal, which is considerably larger than the first error level, in order to generate by this second error level an indication which is suitable for the installation control. A second control device is provided for this. Therefore two control devices are required for controlling the amplitude of the scanning signal after the installation of the scanning head, i.e. for controlling the basic setting, and during the subsequent measuring operation.